the native Christians were allowed nominal freedom of religion with jaziya (tax on non-Muslims, imposed by Muslim rulers) to their rulers for the right to practise their own religion privately. However, the Emirate of Sicily began to fragment as inner-dynasty related quarrels took place between the Muslim regime. By the 11th century, mainland southern Italian powers were hiring ferocious Norman mercenaries, who were Christian descendants of the Vikings; it was the Normans under Roger I who conquered Sicily from the Muslims. After taking Apulia and Calabria, he occupied Messina with an army of 700 knights. In 1068, Robert Guiscard and his men defeated the Muslims at Misilmeri; but the most crucial battle was the siege of Palermo, which led to Sicily being completely in Norman control by 1091. Many historians have recently argued that the Norman conquest of Islamic Sicily (1060–91) was the start of the Crusades. Viking Age In 860, according to an account by the Norman monk Dudo of Saint-Quentin, a Viking fleet, probably under Björn Ironside and Hastein, landed in Sicily, conquering it. Many Norsemen fought as mercenaries in Southern Italy, including the Varangian Guard led by Harald Hardrada, who later became king of Norway, who conquered Sicily between 1038 and 1040, with the help of Norman mercenaries, under William de Hauteville, who won his nickname Iron Arm by defeating the emir of Syracuse in single combat, and a Lombard contingent, led by Arduin. The Varangians were first used as mercenaries in Italy against the Arabs in 936. Runestones were raised in Sweden in memory of warriors who died in Langbarðaland (Land of the Lombards), the Old Norse name for southern Italy. Later, several Anglo-Danish and Norwegian nobles participated in the Norman conquest of southern Italy, like Edgar the Ætheling, who left England in 1086, and Jarl Erling Skakke, who won his nickname ("Skakke", meaning bent head) after a battle against Arabs in Sicily. On the other hand, many Anglo-Danish rebels fleeing William the Conqueror, joined the Byzantines in their struggle against the Robert Guiscard, duke of Apulia, in Southern Italy. High Middle Ages Norman period (1091–1194) The most significant changes that the Normans were to bring to Sicily were in the areas of religion, language and population. Almost from the moment that Roger I controlled much of the island, immigration was encouraged from Northern Europe, France, Northern Italy and Campania. For the most part, these consisted